Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft drives the generator rotor either directly (“directly driven”) or through the use of a gearbox. The operation of the generator produces the electricity to be supplied into the electrical grid.
When maintenance works are required inside wind turbines, hoists are often used in the form of elevator-like structures where a lift platform or a cabin for the transportation of people and/or equipment is hoisted up and/or down within the wind turbine tower. Wind turbines are often provided with working platforms arranged at various heights along the height of the tower with the purpose of allowing workers to leave the cabin and inspect or repair equipment where intended. These sorts of elevator systems are also known in other applications, such as e.g. factories, construction sites, and all sorts of towers.
Elevator systems, in general, include an elevator car being suspended within a hoistway by ropes, cables or belts. In some systems, e.g. some electric elevators, a counterweight may be provided, depending on e.g. the available space. Other systems such as hydraulic elevators normally do not comprise a counterweight. Typically, elevator systems include a moving or travelling cable for supplying electric power to the elevator cabin and/or for signal communication between components associated with the elevator car/cabin and a control panel provided in a fixed location relative to the hoistway.
Elevator systems of the type that are “ladder-guided” or “cable-guided” normally comprise traction and/or safety wire ropes that run free in a direction parallel to the movement of the elevator car.
In use, there may be circumstances in which the traction and/or safety wire ropes may begin to move and sway within an elevator hoistway or the wire ropes can become tangled up in themselves. This is most prominent in high slender structures, such as e.g. tower of larger (MW class) wind turbines, in which the tower may oscillate significantly. In these cases, the traction and/or safety wire ropes can also strike the working platforms, platform fences or tower flanges provided inside the hoistway. Even in some circumstances, e.g. inside a tower of larger wind turbines, the traction and/or safety wire ropes may come in contact with or potentially get entangled with the power cables from the wind turbine generator.
Other circumstances in which the traction and safety wire ropes may come in contact with other components may occur in wind turbine towers in which an elevator path may be curved, e.g. because at the base there is an electronic compartment on one side or because the available space for housing the elevator and e.g. the ladder, requires a change in the orientation of the elevator. Since the traction and safety wire ropes run free, they seek to straighten out. This may result in them striking or interfering with the working platforms, tower flanges or a ladder provided at the hoistway inner surface.
Further circumstances that result in the traction and safety wire ropes touching parts within a tower relate to the shape of the towers. In some cases, a major or minor tapering of the tower is required e.g. due to a change of the material from which the tower is built. For example, a bottom portion of a tower may be made from concrete and an upper portion of the tower may be made from steel. In these situations the distance of the wire ropes to the inner walls of the tower may vary from one section to the other and the orientation of the elevator may need to be changed. Again, as the traction and safety wire ropes seek to straighten out, this may result in the wire ropes striking the working platforms or tower flanges provided on the inner surface of the hoistway.
As mentioned above, in such tall structures, in general, elevator ropes and cables, which may include hoist ropes, compensation ropes, governor ropes, and travelling cables, may vibrate in harmony with the wind induced sway of the structure and other dynamic factors affecting the structure. Particularly in wind turbines, several loads such as for example aerodynamic forces associated with the wind, rotor rotation, etc. may act on the structure. These loads may further be increased in offshore wind turbines by the forces exerted by waves, currents and tides in case of offshore structures.
The aforementioned loads can produce vibrations and sway of the ropes and cables which may cause fatigue and wear, excessive noise, and the increased possibility of tangling thus potentially shortening the lifetime of the ropes and cables and complicating normal operation of the elevator system.
There is thus a need for reliable and effective elevator systems which reduce or eliminate at least some of the afore-mentioned drawbacks.